A traditional high magnetic induction oriented silicon steel comprises the following basic chemical components: 2.0-4.5% of Si, 0.03-0.10% of C, 0.03-0.2% of Mn, 0.005-0.050% of S, 0.02-0.05% of Als (acid-soluble aluminum) and 0.003-0.012% of N, and some component systems further contain one or more of Cu, Mo, Sb, B, Bi and other elements.
A traditional manufacturing method of the traditional high magnetic induction oriented silicon steel comprises the following steps: firstly performing steel making by a converter (or an electric furnace), performing secondary refining and alloying, and performing continuous casting to form a slab; then heating the slab to about 1400° C. in a special high-temperature heating furnace and performing heat preservation for 45 min or more, in order to be conductive to full solid solution of favorable inclusions; then performing hot rolling and laminar cooling, then coiling, precipitating small and dispersed second phase particles in a silicon steel base body in a normalizing process of a hot-rolled plate to obtain effective inhibitors; further performing cold rolling on the hot-rolled plate to the thickness of a finished product, then decarbonizing and annealing to remove C in a steel plate to the degree in which the magnetic performance of the finished product is not affected (which should be 30 ppm or less generally), and coating an annealing isolation agent taking MgO as a main component; further performing high-temperature annealing to realize secondary recrystallization of the steel plate in a high-temperature annealing process, forming a magnesium silicate bottom layer and completing purification treatment (for removing S, N and other elements in steel which are harmful to magnetic property) to obtain the high magnetic induction oriented silicon steel with high degree of orientation and low iron loss; and finally coating an insulating coating, stretching and annealing to obtain an oriented silicon steel product in a commercial application form.
The traditional manufacturing method of the high magnetic induction oriented silicon steel has the following deficiencies: in order to realize full solid solution of the inhibitors, the highest heating temperature needs to reach 1400° C., which is the limit level of the traditional heating furnace. In addition, due to high heating temperature and great burning loss, the heating furnace needs to be repaired frequently and the utilization rate is low. Simultaneously, due to high energy consumption and large edge cracks of a hot-rolled coil, in the cold-rolling procedure, it is difficult to produce, the yield is low and the cost is high.
In view of the above mentioned problems, a large number of studies about reducing the heating temperature of the oriented silicon steel have been developed in the technical field. By differentiating according to the range of heating temperature of the slab, there are two main improvement paths, one is a medium-temperature slab heating process, in which the heating temperature of the slab is 1250-1320° C. and AlN and Cu are taken as the inhibitors; and the other one is a low-temperature slab heating process, in which the heating temperature of the slab is 1100-1250° C., and the inhibitors are introduced by adopting a nitriding method.
At present, the development of the low-temperature slab heating process is faster, for example, the heating of the slab is performed at a temperature of 1200° C. or less, final cold rolling is performed at a cold rolling reduction ratio of more than 80%, and ammonia gas is adopted in the decarbonizing and annealing process to perform continuous nitriding treatment and perform high-temperature annealing to obtain secondary recrystalized grains with relatively high degree of orientation. The manufacturing process has the advantages that the high magnetic induction oriented silicon steel (HiB) can be produced with relatively low cost and the typical magnetic induction B8 of the silicon steel is 1.88-1.92 T.
The inhibitors of the low-temperature slab heating process are mainly from the small and dispersed (Al, Si), N, (Mn, Si) and N particles which are formed by combination of nitrogen and original aluminum in the steel through the nitriding treatment after decarbonizing and annealing. Simultaneously, the inhibitors are also from the existing inclusions in the slab, these inclusions are formed in the steel-making and casting process, realize partial solid solution in the heating process of the slab and are precipitated in the rolling process, and the form of the inclusions can be adjusted by normalizing and annealing, thereby having important influence on primary recrystallization and further affecting the magnetic performance of the final product. When the size of the primary grains is matched with the level of inhibition, the secondary recrystallization is perfected, and the magnetic performance of the final product is excellent. In the normalizing process, although the nitride inhibitors are affected by the form of the inclusions in the slab, it is quite difficult to control the form of the inclusions in the slab, for example, the coarse AlN formed in the casting process is difficult to realize solid solution in the subsequent annealing, thereby causing great difficulty in control of stability of the size of the primary grains and low probability of stably obtaining the high-grade HiB product with the magnetic induction B8 of not less than 1.93 T. In addition, under the condition that the thickness of the finished product is determined, some measures for further reducing the iron loss generally will reduce the magnetic induction, for example, by increasing the Si content or performing laser scribing or the like. The range of applications of these methods for reducing the iron loss is limited due to the reduction in magnetic induction. Other methods for improving the magnetic induction B8, such as fast heating in the decarbonizing and annealing process, need to additionally add special devices such as fast induction heating device or ohmic heating device and the like, and thus the investment cost is increased. In addition, fast heating will increase defects in the bottom layer of the finished product, in particular to the occurrence rate of bright point-like defects.
Chinese patent document with patent publication number of CN1138107A, publication date of Dec. 18, 1996, entitled “High-magnetic flux density and low-iron loss grain oriented electromagnetic steel plate and manufacturing method thereof” discloses an electromagnetic steel plate, which contains 2.5-4.0 wt % of Si and 0.005-0.06 wt % of Al; in all grains of the steel plate, calculated by area rate, at least 95% of the grains are constituted by coarse secondary recrystalized grains with the diameter of 5-50 mm, the (001) axis has an angle of within 5° relative to the rolling direction of the steel plate and the (001) axis has the angle of within 5° relative to the vertical direction of the plate surface; and in the coarse secondary recrystalized grains or a grain boundary, there exist the small grains with the diameter of 0.05-2 mm, and the relative angle of the (001) axis of small grains to the (001) axis of the coarse secondary grains is 2-30°.
Japanese patent document with patent publication number of JP8232020A, publication date of Sep. 10, 1996, entitled “Manufacturing method of directional electromagnetic steel sheet” relates to a manufacturing method for producing a silicon steel sheet with low price and excellent magnetic property, and the manufacturing method includes the steps of performing cold continuous rolling at a specific rolling speed and annealing, regulating to the total nitrogen content at specific ppm and then completing annealing. The steel sheet comprises the following components in weight percent: 0.001-0.09% of C, 2-4.5% of silicon, 0.01-0.08% of acid-soluble aluminum, 0.0001-0.004% of N, 0.008-0.06% of independent or total S and (or) selenium; 0.01-1% of copper, 0.01-0.5% of manganese, a small quantity of Bi, P, Sn, Pb, B, V, niobium and the like and the balance of Fe and other inevitable impurities. The cold continuous rolling ratio of the cold-rolled silicon steel is 75-95%, the annealing temperature is 800-1000° C., the annealing time is 1300 s, and the total nitrogen content is 50-1000 ppm.
Japanese patent document with patent publication number of JP4337029A, publication date of Nov. 25, 1992, entitled “One-time recrystallization sintering method of directional electromagnetic steel plate” discloses a manufacturing method of a directional electromagnetic steel plate, and the manufacturing method mainly relates to a control method of size of primary grains of nitriding of oriented silicon steel, and proposes a method for adjusting decarbonizing temperature according to Als, N and Si.